Power amplifiers may be employed in a variety of electronics applications, including wireless communications. Generally speaking, power amplifiers amplify an input electrical signal to produce an output electrical signal that has increased amplitude relative to the input. Base transceiver stations, enhanced nodes B, and/or cell sites may incorporate one or more radio frequency power amplifiers to boost the power of a signal prior to emitting from an antenna and/or antenna array. Portable electronic devices likewise may incorporate power amplifiers to boost the power of a signal prior to emitting from an antenna. A variety of operating parameters of power amplifiers are of special concern in the wireless environment. For example, regulatory agencies may constrain the emission of spurious signals outside an authorized spectrum of frequencies, thus raising the importance for power amplifiers to reduce spurious spectral emissions. Excess power consumption by power amplifiers is undesirable because this reduces battery life of portable electronic devices, potentially reducing user satisfaction with the devices, and/or increases the expense of operating base transceiver sites, enhanced nodes B, and/or cell sites.
The Doherty amplifier architecture has become widely used as a power amplifier in some wireless communication applications. While the Doherty amplifier may be implemented in a variety different structures, generally the Doherty amplifier comprises a main amplifier and an auxiliary amplifier (also known as a carrier amplifier and a peak amplifier, respectively). In some contexts, the main amplifier may be referred to as a carrier amplifier and the auxiliary amplifier may be referred to as a peaking amplifier. The auxiliary amplifier is operated in a turned off state while the input to the Doherty amplifier remains below an amplitude threshold, and the output of the Doherty amplifier is then provided by the output of the main amplifier alone. The auxiliary amplifier is operated in a turned on state while the input to the Doherty amplifier is at or above the amplitude threshold, and the output of the Doherty amplifier is then provided by the combination of the outputs of both the main amplifier and the auxiliary amplifier. The auxiliary amplifier of the typical Doherty amplifier may be said to be biased for Class C operation.
The LINC (linear amplification with nonlinear components) amplifier features a signal splitter feeding an input having a constant amplitude envelope to each of two amplifiers each producing an output having a substantially constant amplitude envelope. The information content of the input is substantially a phase signal. The outputs of the two amplifiers are combined to produce the output of the LINC amplifier unit, where this output is of varying amplitude by virtue of the input phase modulation and the summing process. The constant envelope input signals promote high efficiency.